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arXiv 1909.08264astro-ph.GA
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在$z>7$用ALMA探测的星系中预期的尘埃粒度分布

Expected dust grain size distributions in galaxies detected by ALMA at $z>7$

Hsin-Min Liu, Hiroyuki Hirashita

摘要:

高红移星系中的尘埃特性为宇宙中尘埃的起源提供了线索。虽然在星系中观测到了红移为$z>7$的尘埃,但仅从尘埃总量来确定主要的尘埃源是困难的。因此,我们计算了粒度分布的演变,期望不同的尘埃源预测不同的粒度分布。利用恒星形成时间尺度和文献数据约束下的重子总质量,计算了粒子尺寸分布的演化。为了解释ALMA探测到的$z>7$星系中的总尘埃质量,以下两种解决方案是可能的:(i)恒星喷出物中的高尘埃凝聚效率,以及(ii)有效的吸积(通过吸积星际介质中的气相金属来增加尘埃)。我们发现,这两种情况下预测显着不同的粒度分布:在(i),灰尘是由大颗粒($a\gtrsim 0.1~μ$ m,其中$a$是颗粒半径)为主,而在(ii),小颗粒($a\lesssim 0.01~μ$ m)的丰度显着增强吸积。因此,预期消光曲线在(ii)中比在(i)中陡得多。因此,我们得出结论,消光曲线提供了一个可行的方法来区分在星系演化的早期阶段占主导地位的尘埃源。

英文摘要:

The dust properties in high-redshift galaxies provide clues to the origin of dust in the Universe. Although dust has been detected in galaxies at redshift $z>7$, it is difficult to constrain the dominant dust sources only from the total dust amount. Thus, we calculate the evolution of grain size distribution, expecting that different dust sources predict different grain size distributions. Using the star formation time-scale and the total baryonic mass constrained by the data in the literature, we calculate the evolution of grain size distribution. To explain the total dust masses in ALMA-detected $z>7$ galaxies, the following two solutions are possible: (i) high dust condensation efficiency in stellar ejecta, and (ii) efficient accretion (dust growth by accreting the gas-phase metals in the interstellar medium). We find that these two scenarios predict significantly different grain size distributions: in (i), the dust is dominated by large grains ($a\gtrsim 0.1~μ$m, where $a$ is the grain radius), while in (ii), the small-grain ($a\lesssim 0.01~μ$m) abundance is significantly enhanced by accretion. Accordingly, extinction curves are expected to be much steeper in (ii) than in (i). Thus, we conclude that extinction curves provide a viable way to distinguish the dominant dust sources in the early phase of galaxy evolution.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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